Hypothermia
The Baltimore Longitudinal Study of Aging (BLSA)
In the Baltimore Longitudinal Study of Aging (BLSA), men with core body temperatures below the median lived significantly longer than men with body temperatures above the median, in the absence of caloric restriction (CR). The BLSA has accumulated almost 30 years of follow-up data in a large population and continues today (Roth et al. (2002) Science 297, 811).
Specifically, in the largest reported longitudinal study of body temperature in humans, it was reported, a decade ago, in men in the BLSA study that participants with core body temperatures in the lower 50% of the study population had significantly lower mortality than those with body temperatures in the upper 50% over 25 years of follow-up (Soare et al. (2011) Aging 3, 374-379).
In humans the average internal temperature is generally considered to be ˜37.0° C. (−98.6° F.), although it varies among individuals. Roth et al. examined the effects of various longevity-related markers from the BLSA. Consistent with the beneficial effects of caloric restriction on aging and lifespan in other animals, men with lower temperatures had greater survival than those with higher temperatures, but the BLSA men were not calorie-restricted.
Furthermore, lower body temperature was reported to be one of only three independent factors influencing longevity (FIG. 1).
The Scripps Research Institute Study
In a 2006 study, scientists at the Scripps Research Institute found that reducing the core body temperature of mice extended their median lifespan, by up to 20% (Conti et al. (2006) Science 314, 825-828). This was the first time that changes in body temperature had been shown to affect lifespan in warm-blooded animals. The study demonstrated that it was possible to increase lifespan in mice by modest, but prolonged, lowering of the core body temperature and that the longer lifespan was achieved independent of caloric restriction.
Prior to this study, researchers had known that core body temperature and aging were related in cold-blooded animals. Scientists had also known that lifespan could be extended in warm-blooded animals by reducing the number of calories they consumed, which also lowered core body temperature as a consequence. However, the degree of caloric restriction needed to extend lifespan is not easy to achieve, even in mice.
Prior to the Scripps study, key questions about the relationship between caloric restriction, core body temperature, and lifespan remained unanswered. Was caloric restriction itself responsible for longer lifespan, with reduced body temperature simply a consequence? Or was the reduction of core body temperature a key contributor to the beneficial effects of caloric restriction?
Mice in the Scripps study were allowed to eat as much food as they wished, and the experimental and control mice ate the same amount suggesting that hypothermia—and not caloric restriction—may be more directly tied to longevity (Conti et al. (2006) Science 314, 825-828). Other examples illustrating and supporting this point follow.
The Naked Mole Rat
Another example of a lower body temperature's effects on aging is the naked mole rat (Heterocephalus glaber), a subterranean, extraordinarily long-lived eusocial mammal (Kim et al. (2011) Nature 479, 223-227). Although the size of a mouse, the naked mole rat's maximum lifespan exceeds 30 years and makes this animal by far the longest living rodent (˜10 times the typical lifespan of comparably sized rodents).
Naked mole rats show negligible senescence, no age-related increase in mortality, and high fecundity until death. In addition to delayed aging, naked mole rats are resistant to both spontaneous cancer and experimentally induced tumorigenesis. They also maintain healthy vascular function longer in their lifespan than shorter-lived rats. The naked mole rat's normal core body temperature is a full 6° C. lower than any other rodent.
It was at first considered that the naked mole rat's exceptional lifespan was associated with its burrowing lifestyle that included intermittent periods of ‘feast’ and prolonged ‘famine’ (calorie restriction). However, the precise reason for their longevity is still debated and is likely the result of many factors.
Longevity was thought to be related to the naked mole rat's ability to substantially reduce its metabolism during hard times, and so to prevent aging-induced damage from oxidative stress. However, when naked mole rats were removed to captivity, they survived to their full potential and remained resistant to disease whether fed their native diet in a feast-famine pattern or a full ad libitum diet, ingested at will. Their core body temperatures, however, remained low. As noted with the Scripps study, the suggestion was that hypothermia—and not caloric restriction—may be more directly tied to the naked mole rat's resistance to disease and remarkable longevity.
Progeria and Progeria-Like Diseases in Children
Progeria, also known as Hutchinson-Gilford Progeria Syndrome (HGPS), is a rare, fatal genetic condition of accelerated aging in children (Gordon et al. (2012) J. Cell Biol. 199, 9-13). All children with progeria die of the same heart disease that affects millions of normally aging adults (arteriosclerosis), but instead of this occurring at 60-70 years of age, the children may suffer strokes and heart attacks even before age 10.
Progeria affects ˜1 in 4-8 million newborns. There are an estimated 200-250 children living with Progeria worldwide at any one time. It affects both sexes equally and all races (Sarkar & Shinton (2001) Postgrad. Med. J. 77, 312-317).
Progeria is a progressive genetic disorder that causes children to age rapidly, beginning in their first 2 years of life. Children with progeria generally appear normal at birth. By 12 months, signs and symptoms, such as slow growth and hair loss, begin to appear. The average life expectancy for a child with progeria is ˜13, but some with the disease die younger and some live 20 years or longer.
Heart problems or strokes are the eventual cause of death in most children with progeria. There is currently no treatment for the condition.
Researchers have discovered a single gene mutation responsible for HGPS. The gene is known as lamin A (LMNA), which encodes a protein necessary for holding the nucleus of a cell together. It is believed that the genetic mutation renders cells unstable, which appears to lead to progeria's characteristic aging process (Gordon et al. (2012) J. Cell Biol. 199, 9-13; Navid et al. (2012) Bioinformation 8, 221-224).
Children with progeria usually develop severe hardening of the arteries. This is a condition in which the walls of their arteries stiffen and thicken, often restricting blood flow. Most children with progeria die of complications related to atherosclerosis, including problems with the blood vessels that supply the heart (cardiovascular problems), resulting in heart attack and congestive heart failure, and problems with the blood vessels that supply the brain (cerebrovascular problems), resulting in stroke (Gerhard-Herman et al. (2012) Hypertension 59, 92-7; Low et al. (2005) BMC Medical Genetics 6, 38).
There are other progeroid syndromes that run in families (Navarro et al. (2006) Hum. Mol. Genet. 15, R151-161). They include, but are not limited to, Wiedemann-Rautenstrauch syndrome (WRS), Werner syndrome (WS), Bloom Syndrome, and Cockayne syndrome (CS). In Wiedemann-Rautenstrauch syndrome, also known as neonatal progeroid syndrome, the onset of aging begins in the womb, and signs and symptoms are already apparent at birth. Werner syndrome typically begins in adolescence or early adulthood.
These inherited progeroid syndromes also cause rapid aging and shortened life span. In the case of Werner syndrome, it has a global incidence rate of <1 in 100,000 live births, although the incidence in Japan and Sardinia is higher, where it affects ˜1 in 20,000-40,000 and ˜1 in 50,000, respectively. In 2006, there were ˜1,300 reported cases of WS worldwide.
Hypothermia and its Relationship with Aging
In recent years, many factors have been theorized to prevent or delay the onset of diseases that affect longevity or to have a direct, independent, or multi-factor inter-related effect on increasing lifespan. Influences such as free radicals, caloric restriction, lowered body temperature, and even components in red wine (e.g., resveratrol) have each been explored.
Even when links have been suggested or established, there remains the practical issue of how to effectively achieve decreased caloric intake, free radical reduction, or the benefits of red wine, for example, without significant lifestyle modifications that must be sustained long-term at often extreme levels and with great difficulty and inconsistency in implementation.
In the case of body temperature reduction, there is presently no practical means of achieving mild and controlled hypothermia (such as a decrease from normal baseline to the range of ˜95° F. to ˜98° F.) that may be of clinical benefit on a chronic-use basis. In fact, studies have shown that a lower average core body temperature by ˜0.2° C., which sounds like a modest reduction, is statistically significant and similar to the reduction observed in long-lived, calorie-restricted mice (Soare et al. (2011) Aging, 3, 374-379).
Although moderate hypothermia induction (a ˜2-4° C. reduction in core temperature) has been established as having clinical benefit, for example in the prevention of organ and neurological damage post-cardiac arrest resuscitation, current methods of achieving hypothermic induction are relatively extreme acute interventions that currently can be accomplished only through the application of artificial ‘forced’ or external methods (e.g., cold blankets, iced saline infusion) accompanied by extreme procedures and processes that, for example, require intubation and ventilatory assistance, heavy sedation and induced paralysis simply to offset the body's natural defense of shivering in response to external attempts to reduce core body temperature.
The ‘mechanical’ or ‘forced’ methodologies in current use are clearly impractical for chronic, routine application and long-term induction of a controlled, regulated reduction in body temperature.
Much evidence of lowered core body temperature's independent effect on prolonging lifespan has emerged in recent years. These findings demonstrate the importance of a reduction of body temperature in modulating longevity.
In the case of the Scripps study, scientists lowered core body temperature directly, without restricting food intake. In cold-blooded animals, such as roundworms (C. elegans) and fruit flies (Drosophila), this task is straightforward; core body temperature can be lowered simply by changing the temperature of the environment.
However, for warm-blooded animals, the task is much more challenging. The Scripps experiment focused on the preoptic area of the hypothalamus, a structure in the brain that acts as the body's thermostat and is crucial to temperature regulation. Just as holding something warm near the thermostat in a room can fool it into thinking that the entire room is hotter so that the air conditioning turns on, the Scripps Research team reasoned that they could reset the brain's thermostat by producing heat nearby. To do so, they created a mouse model that produced large quantities of uncoupling protein 2 in hypocretin neurons in the lateral hypothalamus, near the preoptic area. The action of uncoupling protein 2 produced heat, which diffuses to other brain structures, including the preoptic area. Indeed, the extra heat worked to induce a continuous reduction of the core body temperature of the mice, lowering it from ˜0.3 to ˜0.5° C. The scientists were then able to measure the effect of lowered core body temperature on lifespan, finding that the mice with lowered core body temperature had significantly longer median lifespan than those that did not have a lowered core body temperature.
The researchers performed several experiments to make sure that other factors were not contributing to the lowered core body temperature. They confirmed that the experimental mice were normal in their ability to generate a fever, and that these mice moved around to about the same degree as normal mice. Additionally, the researchers verified that the hypocretin neurons producing uncoupling protein 2 were not involved in temperature regulation. Importantly, the mice in this study were allowed to eat as much food as they wished, and the experimental and control mice ate the same amount (Conti et al. (2006) Science 314, 825-828).
Several other studies have documented a lowering of core body temperature by caloric restriction in mice, rats, and rhesus monkeys. Interestingly, however, ad libitum fed transgenic mice overexpressing the uncoupling protein 2 in hypocretin neurons (Hcrt-UCP2) also had a lower core body temperature and a 16% greater life expectancy than wild-type animals, independent of caloric intake.
Although body temperature is recognized as a clinically useful physiological parameter in the context of infection or extreme environmental exposures, few epidemiological studies have included body temperature as a routine measurement. One consistent observation that has emerged from studies of human body temperature, however, has been that advanced age is associated with lower body temperature.
In the landmark cross-sectional studies of Wunderlich in the 1860s—which included 25,000 participants and established the “normal” body temperature of 98.6° F.—lower body temperatures were observed in elderly participants (Mackowiak et al. (1992) JAMA 268, 1578-1580).
Therapeutic Hypothermia
Hypothermia, as opposed to a modest and controlled reduction in normal body temperature, is a condition in temperature-regulating organisms where the core body temperature is reduced below the normal range. Hypothermia has been used clinically for more than 40 years to protect bodily organs from various pathophysiological insults, including ischemic insults such as cardiac arrest, hemorrhage, hypergravity, and hypoglycemia, and to reduce the toxicity of various drugs and environmental toxicants (Gordon (2001) Ernerg. Med. J. 18, 81-9).
While the precise mechanisms responsible for the therapeutic effects of hypothermia are not fully understood, hypothermia causes a general reduction in cellular metabolism (Polderman (2008) Lancet 371, 1955-69). This reduction during hypothermia is especially beneficial to highly aerobic organs, such as the brain and heart, under ischemic conditions because it leads to reduced demand for oxygen.
Forced hypothermic methods are used for therapeutic hypothermia. Forced hypothermia involves the use of external mechanical and/or endovascular cooling methods to extract heat from the body to reduce the body temperature below the normal temperature set point. External cooling methods include immersing a subject in a cool bath or applying blankets or pads with cooled water circulating through channels in the walls of the blanket or pad to the skin of a subject. Other external methods include wetting of the skin or hair of the subject, cooling the air around the subject, and blowing air across the subject's skin. Endovascular cooling generally involves the rapid intravenous administration of an iced saline solution or heat exchange with a specially designed catheter.
Hypothermia after Cardiac Arrest
In heart surgery, induction of hypothermia (to 28-32° C.) before cardiac arrest has been used successfully since the 1950s to protect the brain against global ischemia.
Successful use of therapeutic hypothermia after cardiac arrest in humans was also described in the late 1950s (Benson et al. (1959) Anesth. Analg. 38, 423-428; Williams & Spencer (1958) Ann. Surg. 148, 462-468; Ravitch et al. (1961) N. Engl. J. Med. 264, 36-38) but was subsequently abandoned because of uncertain benefit and difficulties with its use (Marion et al. (1996) Crit. Care Med. 24, 81S-89S).
More recently, the induction of hypothermia after the return of spontaneous circulation (ROSC) has been associated with improved functional recovery and reduced cerebral histological deficits in various animal models of cardiac arrest (Horn et al. (1991) Acta Neuropathol. (Berl). 81, 443-449; Sterz et al. (1991) Crit. Care Med. 19, 379-389; D'Cruz et al. (2002) J. Cereb. Blood Flow Metab. 22, 848-851; Hicks et al. (2000) J. Cereb. Blood Flow Metab. 20, 520-530). Further preliminary human studies were conducted subsequently (Bernard et al. (1997) Ann. Emerg. Med. 30, 146-153, Sanada et al. (1998) Masui. 47, 742-745, Yanagawa et al. (1998) Resuscitation 39, 61-66, Nagao et al. (2000) J. Am. Coll. Cardiol. 36, 776-783, Zeiner et al. (2000) Stroke 31, 86-94, Felberg et al. (2001) Circulation 104, 1799-1804, Hachimi-Idrissi et al. (2001) Resuscitation 51, 275-281, Callaway et al. (2002) Resuscitation 52, 159-165).
At the time of publication of the American Heart Association/International Liaison Committee on Resuscitation (AHA/ILCOR) 2000 Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care, the evidence was insufficient to recommend use of therapeutic hypothermia after resuscitation from cardiac arrest (AHA/ILCOR (2000) Resuscitation 46, 1-447), but two subsequent studies, one conducted in post-cardiac arrest resuscitated patients in Australia (Bernard et at. (2002) NEJM 346, 557-563) and the second in post-cardiac arrest resuscitated patients conducted by the Hypothermia After Cardiac Arrest Study Group (HACA) in nine European centers (HACA (2002) NEJM 346, 549-556, became the basis for the AHA/ILCOR recommendation for the use of therapeutic hypothermia in the treatment of post cardiac arrest resuscitated patients issued in 2003.                Indeed, the AHA/ILCOR Recommendations, issued in June/July 2003, state that “On the basis of the published evidence to date, the ILCOR ALS Task Force has made the following recommendations:        Unconscious adult patients with spontaneous circulation after out-of-hospital cardiac arrest should be cooled to 32° C. to 34° C. for 12 to 24 hours when the initial rhythm was VF [ventricular fibrillation].        Such cooling may also be beneficial for other rhythms or in-hospital cardiac arrest.”        
Thus, the use of therapeutic hypothermia is now accepted as a standard intervention for the preservation of vital organ systems in the aftermath of cardiac arrest (AHA/ILCOR recommendations).
Therapeutic hypothermia can be achieved mechanically, using medical devices such as, for example, the ThermoSuit®. The ThermoSuit® cools the patient with direct water on skin contact. The water flows over the patient and is returned to the pump. A continuous flow of water is cycled through drawing heat off the body in a much more rapid process than either gel pads or cooling blankets; a treatment period of ˜30 min is usually sufficient to cause a body core temperature reduction of ˜3° C. The suit is portable and is used with a conventional gurney. As the patient reaches the target temperature the water is drawn off the patient and the ThermoSuit® is removed.
While the application of therapeutic hypothermia is accepted as the standard intervention for the preservation of vital organ function in the aftermath of cardiac arrest (AHA/ILCOR recommendation), there is at present no effective pharmacological means to lower and maintain body temperature.
Chronotherapeutics
The existence of circadian rhythms in cardiovascular disease is well-established. It is also known that heart rate and blood pressure normally peak during the morning hours and reach a nadir in the late evening, around bedtime. The incidence of myocardial infarction, stroke, sudden cardiac death, and myocardial ischemia increases during the early-morning hours. Angina attacks occur in a diurnal cycle; their occurrence is common in the hours shortly after an individual begins activity, after waking. Body temperature also follows circadian patterns, where core temperature is typically lower in the morning hours and higher in the afternoon and evening hours.
Based on these relationships, researchers have begun to apply the science of chronotherapeutics, or the timing of drug effect with biologic need, to improve cardiovascular outcomes. Traditional treatment regimens for conditions associated with circadian variation typically do not account for circadian fluctuations in disease activity.
Chronotherapeutic regimens are intended to provide pharmacological intervention at the most appropriate time point(s), in accordance with circadian rhythms. The concept of chronotherapeutics in treating cardiovascular diseases includes dosing traditional agents at specific times throughout the day, the development of new agents, and the development of chronotherapeutic formulations and combinations of drugs with special release mechanisms targeted at inducing the greatest effect during the pre- and post-waking morning surge in heart rate (HR) and blood pressure (BP) and/or, in select populations, during sleep.
Chronotherapeutic agents are specifically intended to provide peak plasma concentrations when their effect is most needed (e.g., in the early morning hours with regard to HR and BP; in the case of regulating body temperature, the reverse may be true). Further, the lowest concentrations of drugs typically occur at night, when HR and BP are typically lowest and, consequently, cardiovascular events are least likely to occur. However, special consideration also needs to be given to overnight levels of the drug(s) for nocturnal hypertensives, and for all hypertensives in the pre- and post-waking hours, where HR and BP (and the calculated RPP, a measure of myocardial oxygen demand and a surrogate predictor of target organ damage and cardiovascular events) rise.
Pharmacological Means for Inducing Therapeutic Hypothermia
There is presently no effective pharmacological means to lower and maintain body temperature over a prolonged period of time. Therapeutic hypothermia is currently restricted to short-term use in acute medical situations that require the induction of mild hypothermia (body temperature in the range of ˜32° C. to ˜34° C.).
For example, US 2012/0282227 A1 (Katz) describes compositions and methods for inducing moderate hypothermia in a subject as an acute, short-term intravenously delivered intervention targeting a therapeutic range of between 32 and 34° C. for 12-24 h duration. However, this is not suitable for chronic, long-term application.
Such acute, mild hypothermia is distinct from modest and controlled hypothermia (a decrease from normal baseline to the range of ˜95° F. to ˜98° F.), which may be of clinical benefit on a chronic-use basis and does not require intravenous administration. The compositions described by Katz are reported to be useful in treating acute clinical insults, including, but not limited to, cerebral ischemic insults, such as post-cardiac arrest resuscitation neurological damage, stroke, spinal cord injury, or traumatic brain injury.
The Katz patent application (US 2012/0282227) also mentions the use of a neurotensin analog, NT69L, for inducing moderate hypothermia. Neurotensin is a 13-amino-acid neuropeptide that regulates the release of leuteinizing hormone and prolactin. An analog of neurotensin refers to a polypeptide analog of neurotensin that may have an amino acid sequence that is longer, shorter, or the same length as the amino acid sequence of neurotensin. Neurotensin analogs may include non-naturally-occurring amino acids and may also include non-amino acid compounds. However, NT69L has hypothermic tolerance issues that would prevent its chronic use.
Methods are also reported to be useful for maintaining regulated mild hypothermia in a subject for a prolonged period of time (i.e., 12-24 h or more) and for reducing the time necessary to induce regulated hypothermia, as compared to mechanical methods of induction (US 2012/0282227).
The compositions or multidrug combinations of Katz′ invention comprise a regulated hypothermic compound or a dopamine receptor agonist, a vasoactive compound, and an anti-arrhythmic compound or a serotonin 5-HT3 receptor antagonist.
As an example, the patent application describes                A composition comprising:        a regulated hypothermic compound or a dopamine receptor agonist,        a vasoactive compound, and        an anti-arrhythmic compound or a serotonin 5-HT3 receptor antagonist.        
Various combinations of drug components are described. In some examples, the compositions comprise ethanol and optionally at least one of a vasoactive compound, an anti-hyperglycemic compound, a dopamine receptor agonist, an anti-arrhythmic compound, a serotonin 5-HT3 receptor antagonist, an anti-oxidant, a vitamin, and N-acetylcysteine.
In the examples where the composition or multidrug combination comprises ethanol and optionally additional agents, the method of administration requires a two-phase method of delivery of the composition. The invention described further recognizes that a two phase delivery, a delivery of a high concentration of the multidrug combination followed by delivery of a lower concentration of the multidrug combination. This two phase method of delivery may be accomplished by a rapid infusion of the composition to induce hypothermia followed by a period of slow infusion, rapidly reducing the body temperature of a patient and maintaining the hypothermic state for a sustained period of time. Using this method of delivery, the composition may comprise a regulated hypothermic compound or a dopamine receptor agonist, a vasoactive compound, and an anti-arrhythmic compound or a serotonin 5-HT3 receptor antagonist and additional additives, as discussed above.
Additionally, using the two-phase method of delivery, the composition may comprise ethanol and at least one of a vasoactive compound, an anti-arrhythmic compound, a serotonin 5-HT3 receptor antagonist, an anti-oxidant, a vitamin, N-acetylcysteine, and an anti-hyperglycemic compound. This two-phase delivery method can be used to deliver any of the compositions of the invention and provides significant benefits to a patient.
The methods disclosed include a method for inducing hypothermia in a subject comprising administering to the subject a multidrug combination comprising a regulated hypothermic compound or a dopamine receptor agonist, a vasoactive compound, and an anti-arrhythmic compound or a serotonin 5-HT3 receptor antagonist.
In those embodiments where the clinical insult is of an acute nature, the methods were capable of preventing or limiting permanent injuries or stress, particularly if used within the first few hours after the clinical insult. The methods were reported to be useful in treating patients suffering from brain injuries, heart injuries, kidney injuries, cardiac bypass patients, patients suffering cardiac arrest, patients with neurologic injury, infants with hypoxic-ischemic encephalopathy, and injuries of vital organs related to ischemia-reperfusion. Thus, these methods can be used to reduce the stress and discomfort of shivering and to positively benefit and prevent injuries to the brain, heart, kidneys, and other organs. The methods lead to a reduction in mortality or a reduction in adverse effects attributed directly or indirectly to the clinical event.
Studies have shown that a lower average core body temperature by ˜0.2° C., which is a modest reduction, is statistically significant and similar to the reduction observed in long-lived, calorie-restricted mice (see Soare et al. (2011) Aging 3, 374-379). In the case of body temperature reduction, there is presently no practical means of achieving and sustaining such modest and controlled hypothermia (a decrease from normal baseline to the range of ˜95° F. to ˜98° F.) that may be of clinical benefit on a chronic-use basis.
Thus, there is a continuing need to provide drugs or drug products that safely lower body temperature by BLSA study amounts (˜95° F. to ˜98° F.), suitable for chronic low-dose use.
Embodiments of the present invention address that continuing need, providing effective pharmacological means to achieve modest and controlled hypothermia (a decrease from normal baseline to the range of ˜95° F. to ˜98° F.).